Process for preparing electroactive insertion compounds and electrode materials obtained therefrom

ABSTRACT

A process for preparing an at least partially lithiated transition metal oxyanion-based lithium-ion reversible electrode material, which includes providing a precursor of said lithium-ion reversible electrode material, heating said precursor, melting same at a temperature sufficient to produce a melt including an oxyanion containing liquid phase, cooling said melt under conditions to induce solidification thereof and obtain a solid electrode that is capable of reversible lithium ion deinsertion/insertion cycles for use in a lithium battery. Also, lithiated or partially lithiated oxyanion-based-lithium-ion reversible electrode materials obtained by the aforesaid process.

RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.12/953,077, filed on Nov. 23, 2010, which is a continuation of U.S.application Ser. No. 12/418,176, filed on Apr. 3, 2009, which is acontinuation of U.S. application Ser. No. 10/536,431, filed on Nov. 16,2005, which is a national stage application of International ApplicationNo. PCT/CA2004/002182, filed Dec. 22, 2004, which claims priority toU.S. Provisional Application No. 60/531,606, filed Dec. 23, 2003. Thecontents of U.S. application Ser. No. 12/953,077, U.S. application Ser.No. 12/418,176, U.S. application Ser. No. 10/536,431, InternationalApplication No. PCT/CA2004/002182, and U.S. Provisional Application No.60/531,606 are incorporated herein by reference.

TECHNICAL FIELD

The invention relates to a process for preparing transition metalphosphate based electroactive compounds for battery application and tomaterials made by said process, such as LiFePO₄ and non-stoichiometricor doped LiFePO₄ and other analog phosphates for use in lithiumbatteries.

BACKGROUND ART

Transition Metal Phosphate-Based Electrode Materials for LithiumBatteries and their Synthesis

Since Goodenough pointed out the value of lithium ion reversible ironphosphate-based electrodes for use in lithium and lithium-ion batteries(J. Electrochemical Society, vol. 144, No. 4, pp. 1188-1194 and U.S.Pat. Nos. 5,810,382; 6,391,493 B1 and 6,514,640 B1) several groups havedeveloped synthesis processes for making lithiated iron phosphates ofthe ordered-olivine, modified olivine or rhombohedral nasicon structuresand other chemical analogs containing transition metals other that iron.

Until now most processes and materials described in the art tomanufacture electrochemically active phosphate-based electrodes for usein battery applications are based on solid state reactions obtained withiron⁺² precursors intimately mixed with lithium and phosphate containingchemicals that are used individually or as a combination thereof. Iron⁺²oxalate and acetate are the more frequently used starting materials forsyntheses carried out under an inert or partially reducing atmosphere toavoid transition metal oxidation to a higher level, e.g. Fe⁺³ forexample (see Sony PCT WO 00/60680A1 and Sony PCT WO 00/60679 A1).LiFePO₄ active cathode materials with improved electrochemicalperformance were also obtained using C introduced as an organicprecursor during material synthesis (Canadian Application No. 2,307,119,laid-open date Oct. 30, 2000). Addition of carbon powder or C-coating toLiFePO₄ increases powder electronic conductivity, normally in the rangeof 10-9-10-10 Scm⁻¹ for pure LiFePO₄ at ambient temperature. Morerecently, solid-state syntheses of LiFePO₄ obtained from Fe⁺³ precursorssuch as Fe₂O₃ or FePO₄ have been described. These syntheses use reducinggases or precursors (PTC/CA2001/001350 published as WO 02/27824 andPTC/CA2001/001349 published as WO 02/27823) or are carried out by directreduction (so-called carbothermic reduction) of mixed raw chemicals withdispersed C powder (Valence, PCT WO 01/54212 A1).

All of these solid-state synthesis reaction ways require relatively longreaction time (several hours) and intimate mechanical dispersion ofreactants since the synthesis and/or particle growth in the solid stateare characterized by relatively slow diffusion coefficients.Furthermore, particle size, growth, and particle size distribution ofthe final electrode material are somewhat difficult to control fromchemical precursors particle dimensions or in view of thereactive-sintering process, partially suppressed by the presence ofdispersed or coated carbon on reacting materials.

Recent attempts to grow pure or doped LiFePO₄ in solid state and at hightemperature, for example 850° C., have led to iron phosphate with 20micron single grain sized, intimately mixed with iron phosphideimpurities and with elemental C thus making intrinsic conductivityevaluation difficult (Electrochemical and Solid-State Letters, 6,(12),A278-A282, 2003).

None of the previously demonstrated synthesis procedures to makeLiFePO₄, doped or partially substituted LiFePO4 and transition metalphosphate-based analogs as electrode materials, contemplate a directmolten state phase process in which a liquid, phosphate-containing phaseis used to achieve synthesis, doping or simply to melt and prepareelectrochemically active lithiated or partially lithiated transitionmetal phosphate-based electrode materials, especially phosphate-basedmaterials made of iron, manganese or their mixtures obtained in a denseform as a result of a melting/cooling process, optionally comprising oneor more synthesis, doping or partial substitution steps.

In fact most known synthesis work on phosphates for use as electrodematerial suggest working at low temperature to avoid rapid particlegrowth in the solid state and partial decomposition of the ironphosphate under reducing conditions as such or irreversibledecomposition of the precursor chemical at too high a temperature.

Metal Phosphates Preparation by Melting Process

Although inorganic phosphates, pyrophosphates or phosphorous pentoxidehave been used with iron oxide and other oxides, to melt and stabilizeby vitrification, hazardous metal wastes such as alkali and alkalineearth radioactive elements (U.S. Pat. No. 5,750,824) the chemicalformulation of the melt obtained at a temperature in the range of1100-1200° C., is variable with both Fe⁺² and Fe⁺³ being present. Thepurpose was indeed to obtain a stable vitreous composition and not aspecific formulation and structure that are appropriate forelectrochemical activity, i.e. capable of high reversible lithium-ioninsertion-desinsertion.

Additional literature on ferric-ferrous or Mn⁺²—Mn⁺³ ratios observed insodium oxide-phosphorus pentoxide melts at lower temperature, forexample 800° C., is also found in Physics and Chemistry of Glasses(1974), 15(5), 113-5. (Ferric-ferrous ratio in sodium oxide phosphoruspentoxide melts. Yokokawa, Toshio; Tamura, Seiichi; Sato, Seichi; Niwa,Kichizo. Dep. Chem., Hokkaido Univ., Sapporo, Japan. Physics andChemistry of Glasses (1974), 15(5), 113-15.)

A Russian publication describes the growth of LiCoPO₄ crystals in airfrom LiCl—KCl-based melts containing lithium pyrophosphate in order tomake X-ray diffraction studies, but no mention or suggestion is made asto the use of melts in a process to prepare electrochemically activelithium-ion inserting phosphate cathodes containing air sensitive ironfor use in lithium-ion batteries. Synthesis and x-ray diffraction studyof the lithium cobalt double orthophosphate LiCoPO 4. Apinitis, S.;Sedmalis, U. Rizh. Tekhnol. Univ., Riga, USSR. Latvijas PSR ZinatnuAkademijas Vestis, Kimijas Serija (1990), (3), 283-4.

Another work by Russian authors describes crystal growth from melt ofM⁺³ (including isovalent and heterovalent cations) phosphates for use assuperionic conductors including ferric phosphate of the formulaLi₃Fe₂(PO₄)₃. Nowhere it is shown or even suggested that such materialcan be electrochemically active as an electrode material, furthermore,their formulations including isovalent metals are not adapted for suchuse. Furthermore, these phosphate containing materials are fullyoxidized and of no use in a lithium-ion battery normally assembled indischarged state (with the transition metal in its lower oxidation stateand the reversible lithium-ions present in the electrode after materialsynthesis). Synthesis and growth of superionic conductor crystals Li ₃ M₂(PO ₄)₃(M=Fe ^(3+,) Cr ^(3+,) Sc ³⁺). Bykov, A. B.; Demyanets, L. N.;Doronin, S. N.; Ivanov-Shits, A. K.; Mel'nikov, O. K.; Timofeeva, V. A.;Sevast'yanov, B. K.; Chirkin, A. P. Inst. Kristallogr., USSR.Kristallografiya (1987), 32(6), 1515-19.

None of the previous art teaches how to make a lithiated phosphateelectrode using a simple and rapid process in which phosphate cathodeformulations are prepared in the molten state and cooled in order toobtain a solid cathode material having electrochemical properties thatare optimized for use in lithium batteries, especially lithium-ionbatteries (synthesis in the discharged or partially discharged state).In fact, previous art on phosphate-based cathode materials suggests thatas low a temperature as possible (450-750° C.) is better to achieve goodelectrochemically active formulation and stoichiometry, for example:LiFePO₄ formulation with adequate particle size and optimalelectrochemical activity, while avoiding total iron reduction to Fe° orsimple thermal decomposition of the iron or other metal phosphate tooxide and P₂O₅ or to iron phosphides at temperature higher than 850-950°C. In fact, the melting of pure lithiated phosphates, not to sayelectrochemically active ones, without partial or total decompositionwas not expected or described; neither, a fortiori, a process combiningchemical synthesis and phosphate cathode formulation melt.

DISCLOSURE OF THE INVENTION

New Process for Making Pure, Partially Substituted or Doped LithiatedTransition Metal Phosphate Cathodes

The present invention relates to a new process based on the use of amolten phase, preferably a molten phosphate-containing liquid phase, toobtain lithiated or partially lithiated transition metal oxyanion-based,such as phosphate-based, electrode materials. The process comprises thesteps of providing a precursor of the lithium-ion reversible electrodematerial, heating the electrode material precursor, melting it at atemperature sufficient to produce a melt comprising an oxyanion, such asphosphate, containing liquid phase, and cooling the melt underconditions to induce solidification thereof, and obtain a solidelectrode material that is capable of reversible lithium iondeinsertion/insertion cycles for use in a lithium battery. Any one ofthese steps may be carried out under a non reactive or partiallyreducing atmosphere. According to a preferred embodiment, the processmay include chemically reacting the precursor when heating and/ormelting same.

As used in the present description and claims, the term precursor meansan already synthesized at least partially lithiated transition metaloxyanion, preferably phosphate, electrode material or naturallyoccurring lithiated transition metal oxyanion, preferably phosphateminerals, such as triphylite, having the desired nominal formulation or,a mixture of chemical reactants containing all chemical elementsrequired for making, when reacted, an at least partially lithiatedtransition metal oxyanion, such as phosphate-based, electrode materialof the right formulation. The mixture may contain other metal andnon-metal element additives or reductant chemicals such as C or othercarbonaceous chemicals or metallic iron, or mixtures thereof.

According to a preferred embodiment of the invention, the temperature atwhich the molten phosphate containing phase is obtained, is between themelting point of the lithiated transition metal phosphate material and300° C. above, more preferably less that 150° C. above that temperature,in order to limit thermal decomposition or further reduction of thereactants or final product in the presence of reducing chemicals, suchas C or gases. Another advantage of limiting the temperature above themelting temperature of the final product is to avoid energy cost andhigher cost of furnace equipment when the temperature exceeds 1200° C.

According to another embodiment of the invention, the temperature atwhich the molten phosphate containing phase is obtained, is between afixed temperature between 300° C. above the melting point of thelithiated transition metal phosphate material and 200° C., morepreferably 100° C. under that melting point, in which case the finallithiated transition metal phosphate is solidified from the melt uponcooling.

The process according to the invention may also be used for preparing alithiated or partially lithiated transition metal oxyanion-basedelectrode materials of the nominal formula AB(XO₄)H, in which

A is lithium, which may be partially substituted by another alkali metalrepresenting less that 20% at. of the A metals,

B is a main redox transition metal at the oxidation level of +2 chosenamong Fe, Mn, Ni or mixtures thereof, which may be partially substitutedby one or more additional metal at oxidation levels between +1 and +5and representing less than 35% at. of the main +2 redox metals,including 0,

XO₄ is any oxyanion in which X is either P, S, V, Si, Nb, Mo or acombination thereof,

H is a fluoride, hydroxide or chloride anion representing less that 35%at. of the XO₄ oxyanion, including 0.

The above electrode materials are preferably phosphate-based and mayhave an ordered or modified olivine structure.

The process according to the invention may also be used for preparing anelectrode material of the nominal formula Li_(3-x)M′_(y)M″_(2-y)(XO₄)₃in which: 0≦x<3, 0≦y≦2; M′ and M″ are the same or different metals, atleast one of which being a redox transition metal; XO₄ is mainly PO₄which may be partially substituted with another oxyanion, in which X iseither P, S, V, Si, Nb, Mo or a combination thereof. The electrodematerial preferably has the characteristics of the rhombohedral Nasiconstructure.

As used in the present description and claims, the term “nominalformula” refers to the fact that the relative ratio of atomic speciesmay vary slightly, in the order of 0.1% to 5% and more typically from0.5% to 2%, as confirmed by a common general XRD pattern and by chemicalanalysis.

The process according to the invention may also be used for preparing aphosphate-based electrode material having the nominal formulaLi(Fe_(x)Mn_(1-x))PO₄ in which 1≧x≧0, which is capable of conductingelectricity.

In general, the process and material of the invention can be used tomanufacture most of transition metal phosphate-based electrode materialscontemplated in previous Patent and Applications such as describedwithout limitation in U.S. Pat. Nos. 5,910,382; 6,514,640 B1, 6,391,493B1; EP 0 931 361 B1, EP 1 339 119, and WO 2003/069 701.

The process according to the invention can provide lithiated orpartially lithiated transition metal phosphate-based electrode materialsthat have a partially non-stoichiometric nominal formula, provide solidsolutions of the transition metal or of the oxyanion, or slightly dopednominal formula with improved electronic conductivity, and optionallyimproved ion-diffusion characteristics. The term “improved electronicconductivity” as used in the present description and claims means, inthe case of LiFePO₄, the improved capacity of the cathode material toconduct electricity by more than one order of magnitude as compared tothe conductivity of LiFePO₄ obtained by a solid-state synthesis reactionwithout using any electronic conductivity additive or a phosphatecapable of dissipating a charge under SEM observation (without in thiscase the use of any C or other electronically conductive coatingadditive, SEM observation that cannot be achieved with purestoichiometric LiFePO₄ material with no conductivity additive forexample).

The invention provides a new synthesis process based on the use of amolten phase, preferably a molten phosphate-rich phase, to makelithiated or partially lithiated transition metal phosphate-basedelectrode materials, wherein the lithiated or partially lithiatedtransition metal phosphate-based electrode formulations are preferred,first because they are well suited for use in lithium batteriesassembled in their discharged (lithiated) state, second, because alithiated (reduced) electrode formulation allows greater thermalstability to some phosphate crystal structure and also to theircorresponding molten form.

According to a preferred embodiment of the present invention, the moltenphase comprises at least the cathode material in its molten state beforesolidification and is obtained by chemically reacting the precursorduring the heating or melting steps or simply by melting the precursorwhich in this case already comprises the at least partially lithiatedtransition metal phosphate based cathode material.

According to another preferred embodiment of the invention, theatmosphere used during at least the steps of heating and melting is apartially reductive atmosphere. By partially reductive atmosphere, werefer to the fact that the atmosphere comprises gases such as CO, H₂,NH₃. HC and also CO₂, N₂, and other inert gases in a proportion and attemperature selected so as to bring or maintained the redox transitionmetal at a fixed oxidation level, for example +2 in the AB(XO₄)Hcompounds, without being reductive enough to reduce said redoxtransition metal to metallic state. By HC we mean any hydrocarbon orcarbonaceous product in gas or vapor form.

In the present description and claims, the term “redox transition metal”means a transition metal that is capable of having more than oneoxidation state higher than 0, e.g. Fe⁺² and Fe⁺³, in order to act as anelectrode material by reduction/oxidation cycle during batteryoperation.

According to another embodiment of the invention, an inert or nonreactive atmosphere is used and only the thermal conditions and thepresence of lithium in the molten transition metal based phosphate phaseis used to stabilize the redox transition metal in its desired oxidationstate, e.g. Fe⁺² in the case of Li FePO₄.

Another preferred embodiment of the invention is characterized thepresence of C or a solid, liquid or gaseous carbonaceous material duringat least one of the steps of heating, optionally reacting, and melting,optionally reacting, the electrode precursor. Said C should bechemically inert or compatible (low reactivity) with reaction productsduring the synthesis, optionally it should be capable of trappingingress of oxygen traces to keep the redox transition metal in itsoxidation state of +2 or in some cases capable of partially or totallyreducing the redox transition metal to its oxidation state of +2.

Another preferred embodiment of the invention is characterized by thefact that one or more solid-liquid or liquid-liquid phase separationsoccur during the melting step thus allowing separation and purificationof the molten cathode material from other impurities including C powder,Fe₂P, unreacted solids or other solids or liquid non miscible phases,that are present in other phases non-miscible with the liquid moltencathode material. Alternatively, the invention allows for separation andpurification during the cooling step where impurities or decompositionproducts that are soluble in the molten phase can be rejected during thecooling and crystallization step.

According to the process of the invention doping or substitutionelements, additives, metals, metalloids, halides, other complexoxyanions (XO₄), and oxide-oxyanions (O—XO₄) systems, where X may be nonlimitatively Si, V, S, Mo and Nb can be incorporated with the cathodematerial formulation during the heating, and/or reacting steps or,preferably, while the lithiated transition metal phosphate-basedelectrode material is in molten state. Examples of doped,non-stoichiometric or partially substituted formulations contemplated bythe present invention include but are not limited to those disclosed inU.S. Pat. No. 6,514,640 B1. Other doping effects resulting, for example,from the partial solubility of products resulting from the thermaldecomposition of the phosphate electrode precursor are also included inthe process and materials of the present invention.

According to another embodiment of the invention, the cooling andsolidification step is rapid in order to quench the liquid phase andobtain otherwise metastable non-stoichiometric electrode formulation ordoped compositions.

Another of the materials obtained with the process of the invention isthe fact that they have intrinsic electronic conducting properties,optionally ionically enhanced Li+ ion diffusion properties while havingpure nominal formulation, possibly but not limitatively as a result ofsome degree of non-stoichiometry with some lithium and transition metalsite reciprocal substitution.

Another preferred embodiment of the invention is based on the controlledcooling and crystallization of the molten lithiated transition metalphosphate phase also containing other additives or impurities in orderto precipitate such additive or impurities during crystallization orother subsequent thermal treatment in order to make an intimately mixedcomposite material made of crystallites of the lithiated transitionmetal phosphate cathode material intermixed with at least another phasecontaining additive or impurities, said phase having electronic orLi+ion diffusion enhancing properties when the composite material isused as an Li−ion reversible electrode.

According to another preferred embodiment of the invention the electrodeprecursor material comprises a mixture of chemicals containing allelements required and selected to react chemically to give essentiallythe phosphate-based cathode formulation while in the liquid state.Preferably the chemical used for the electrode precursor are low cost,largely available commodity materials or naturally occurring chemicalsincluding in the case of LiFePO₄, iron, iron oxides, phosphate mineralsand commodity lithium or phosphate chemicals such as: Li₂CO₃, LiOH,P₂O₅, H₃PO₄, ammonium or lithium hydrogenated phosphates. Alternativelythe chemical are combined or partially combined together to facilitatethe synthesis reaction during the heating or melting steps. Carbonaceousadditive, gases or simply thermal conditions are used to control theredox transition metal oxidation level in the final lithiated product.

In another embodiment, the process is characterized by the fact that themolten process is carried out in the presence of a C crucible and lidand uses an inert or slightly reductive atmosphere at a temperatureranging preferably between 700 and 1200° C., more preferably between 900and 1100° C. Alternatively a somewhat lower temperature can be used if amelting additive is used during the heating and/or melting steps. Bymelting additive one means low temperature melting phosphate chemicals(e.g. P₂O₅, LiH₂PO₄, Li₃PO₄, NH₄H₂PO₄, Li₄P₂O₇, for example) or otherlow temperature melting additive, LiCl, LiF, LiOH that may contributesto the final phosphate-based electrode formulation during the meltingstep or after the cooling step.

One important alternative of the invention is characterized by the factthat redox transition metal can be kept at a its lower, lithiated orpartially lithiated discharged state during the heating, optionallyincluding a reacting step and during the melting, optionally including areacting step without any reductant additive, such as C, and under aninert atmosphere by the sole use of a heating and melting temperaturehigh enough to insure thermal stability or reduction of the redox metalat the lower discharged state in a chemical formulation stabilized bythe presence of lithium ion. Some embodiments of the invention confirmthe fact that LiFePO₄ or Li(FeMn)PO₄ mixtures for example can besynthesized and/or melted indifferently from a Fe⁺², from a Fe⁺²/Fe⁺³mixture, from a Fe°/Fe+3 mixture or a purely Fe⁺³ containing precursor,and this without C or other reductive additives or atmospheres.

Advantages of the Invention

Some of the advantages of a process (and material so obtained) based onthe melting of a lithiated or partially lithiated redox transition metaloxyanion, such as phosphate-based formulation and of the electrodematerials obtained thereby will appear from the following examples ofthe present invention.

To one skilled in the art, a molten-phase manufacturing process offersthe possibility of a rapid and low cost process to synthesize ortransform phosphate based electrode materials as opposed to asolid-state synthesis and/or a sintering reaction. Furthermore,chemically combining the precursor components before and especiallyduring the melting step allows for a direct melt-assisted synthesis froma large range of available commodity chemicals, including naturallyoccurring minerals as starting reactants.

Despite the fact that the melting step is usually carried out atrelatively high temperature, for example between 900-1000°, the processallows a solid-liquid or liquid-liquid phase separation that contributesto lithiated transition metal phosphate-based electrode materialpurification when the precursor is already a crude lithiated transitionmetal phosphate-based made by synthesizing chemical elements that forman impure liquid phase of the lithiated transition metal phosphatematerial. All means of heating known to the specialist are contemplatedby the present invention including combustion, resistive and inductiveheating means applicable to a large batch or to a continuous process.

The process can be carried out in the presence of C or other reducingadditives or atmospheres or without any reducing agent, by simplyselecting the temperature at which the electrode material is heated andmelted thus allowing different conditions for preparing differentlithiated phosphate-based electrode materials with different redoxmetals and different defective or doped crystal structures.

The melting and cooling steps result in electrode materials of arelatively high particle top density form in a range of differentparticle sizes and distributions as obtained by grinding, sieving andclassifying by means known in the battery, paint or ceramic art.

Furthermore, pure, doped, or partially substituted electrode material ofcomplex formulations can be made easily and rapidly throughsolubilization of the additive elements in the molten phase, which arethereafter cooled and solidified in their crystalline form to expelpartially or totally the additives from the crystal structure or,alternatively, in their amorphous or crystal defective form by rapidquenching for example in order to optimize electronic conductivity orLi−ion diffusion. A preferred mode of realization is take advantage ofthermal treatment of additive solubility in the molten phase to formdoped electrode material containing the lithiated transition metalphosphate-based electrode material and/or or composite material with aseparate phase containing part or totality of the additive. Such dopedor composite electrode material having improved electronic conductivityor improved Li−ion diffusivity.

The process of the invention also allows reprocessing or purifying ofsynthetic lithiated or partially lithiated transition metalphosphate-based electrode materials or alternatively of lithiatedtransition metal phosphate natural ores at any steps of theheating/melting/cooling process.

Another characteristic of the invention is to allow ease of control ofthe particle size and distribution by first melting, then cooling densephosphate-based electrode materials followed by any of appropriateconventional crushing, grinding, jet milling/classifying/mecanofusiontechniques. Typical particle or agglomerate sized that are available toone skilled in the art range between hundredth or tenth of a micron toseveral microns.

Since the process allows to synthesize a pure electrode material,especially without C, any ulterior C coating or addition independentlyof the synthesis process as well as any other surface treatment known toone skilled in the art becomes easy to make and control.

A process based on a molten step allows major process simplificationsversus other known solid state processes for making phosphate-basedcathode materials since the molten process of the invention allows theuse of mixtures of largely available raw chemicals or even of naturalminerals as well as of pre-synthesized electrode materials as precursor.Presently, known solid state reaction processes require intimate mixingof the reactant powders and relatively long residence time for thesynthesis reaction to be completed. On the contrary, a molten phase athigh temperature allows rapid mixture and synthesis reaction as well asthe introduction of additives, substitution elements and dopants in themolten state.

More specifically the molten state facilitates the manufacture ofoptimized, doped, partially or totally substituted lithiated orpartially lithiated phosphate cathode materials containing other metal,halide or oxyanions (XO₄) or oxide-oxyanion other that pure phosphates.

One very important characteristic of the process of the invention isthat it was found possible to obtain an electrode material of improvedelectrical conductivity and possibly of greater Li−ion diffusivity, forexample intrinsically electronic conductive LiFePO₄ was obtained withthe process of the invention, i.e. without doping LiFePO₄ with otherelements than Li, Fe, P and O. Most probably but without limitation,this is the result of an off-stoichiometric composition and/orreciprocal ion site substitution.

Similarly, phosphate-based electrode formulations such as Li(FeMn)PO₄,LiFe_((0.9))Mg_((0.1))PO₄ or doped LiFePO₄ were prepared according tothe present invention to allow for an optimization of electronicconductivity and high Li−ion diffusion.

In addition to the fact that the present invention allows to use lesscostly Fe precursors (Fe, Fe₂O₃, Fe₃O₄, FePO₄ instead of Fe⁺²phosphates, acetate, oxalates, citrates, etc), the invention also makesit possible to design new structures not available by other solid-stateprocess, e.g., liquid-phase solubilization, substitution and dopingfollowed by quenching or thermal treatment to achieve controlledcrystallization or precipitation among others.

Another particularity of the invention is that it offers the possibilityto use less pure precursors such as FePO₄ or LiFePO₄ with largerstoichiometry ratio window and/or with any Fe³⁺/Fe²⁺ ratio since thephase separation in the molten state combined with the heating andmelting step temperature can correct stoichiometry, formulation incombination or not with cooling solidification process.

Depending on the redox metals used for the lithiated or partiallylithiated phosphate-based formulations, the invention offers thepossibility to work under normal air, or in the case of iron containingmaterial, just by using a C container and C lid and simply limitingexposition to air during the heating, melting and cooling steps of theprocess.

The process of the invention encompass the possibility to preparedinorganic-inorganic composite based on the use of a molten phase thatmight comprise impurities or additive soluble only in the molten state,more that one liquid molten phase or that might comprise an additionalsolid phase co-existing with the molten phase thus resulting uponcooling in a composite system containing the solid transition metalphosphate-based electrode material lithiated or partially lithiated andintimately mixed with another solid phase having beneficialelectronically or ionically conducting characteristics as an electrodematerial. Interesting electrochemical results have been achieved alsousing Cr and especially Mo additive in order to create doped orcomposite electrode materials made of more or less doped LiFePO4 with aMo containing phase excluded from the LiFePO4 structure during thermalcooling from the molten state.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged photography of a C-coated LiFePO₄ pressed pelletafter melting, showing phase separation between a liquid molten phaseand a C containing solid crust-phase.

FIG. 2 shows XRD diagrams of original un-melted C-coated LiFePO₄ and ofthe melted phase showing LiFePO₄ pattern.

FIG. 3 is a cyclic voltametric diagram (20 my/h) of a polymerelectrolyte battery test at 80° C. and using carbonated LiFePO₄-melt ascathode; incremental capacity (dQ) is provided in function of voltageLi⁺/Li⁰.

FIG. 4 is an enlarged SEM photo of melt triphylite ore top surfaceproviding composition of main phases determined by X-rayu analysis.

FIG. 5 is an enlarged SEM photo of melt triphylite ore slice and surfacemapping composition for Si, Al, and Ca.

FIG. 6 is an enlarged SEM photo of Mo doped LiFePO₄-melt and Mo surfacemapping composition both before and after tempering (quenching).

FIG. 7 is a power test of a liquid electrolyte battery usingLiFePO₄-melt as cathode; cathode capacity has been normalized withnominal capacity (159.9 mAh/g) and determined for various discharge ratexC, x representing time to discharge nominal capacity in 1/x hours.

EXAMPLES Example 1 Preparation of LiFePO₄ from Carbon Coated GradeIncluding a Liquid-Molten Phase Step

Pure carbon coated LiFePO₄ crystals with ≈1.6% wt. carbon coating(designated “LiFePO₄—C”), made by solid-state reaction between FePO₄,Li₂CO₃ and an organic carbon coating precursor in reducing atmosphere,according to PCT Application WO 02/27823 A1, has been obtained fromCanadian corporation Phostech Lithium Inc (www.phostechlithium.com). 30g of this compound mixed with ≈10% wt. glycerin was pressed under 55,000lbs during 5 minutes to give a ≈3″ diameter and ≈8 mm thickness pellet.This pellet was then deposited on an alumina ceramic plate and heated inan airtight oven chamber, maintained under argon with a continuous flowof gas, from ambient temperature to 950° C.±30° C. in 4 hours, left 4hours at 950° C.±30° C. and then cooled from 950° C.±30° C. to ambienttemperature in 8 hours. A grey molten mineral phase was observed, withlarge crystals formed on cooling that has flowed on most of the ceramicsupport. Surprisingly, this molten phase has separated from anothercarbon-based crust phase that has preserved the shape of the originalpellet but with a smaller ≈1″ diameter (See FIG. 1). The melted mineralmaterial of the melted phase was then separated from its carbon crustfor analysis. X-ray diffraction (XRD) especially proved thatsurprisingly the melt phase was found to consist mainly of LiFePO₄(identified as “LiFePO₄-melt”). Phase composition results as determinedby XRD of the LiFePO₄-melt powder, obtained by grinding crystals in amortar, are summarized in Table 1 in comparison to composition resultsfor the original carbon coated LiFePO₄ before the melting step. The XRDspectra of powdered LiFePO₄-melt is provided in FIG. 2 as compared tothe XRD spectra of LiFePO₄—C before heat treatment.

TABLE 1 XRD composition of LiFePO₄ before and after treatment with atentative attribution of the minor phase. Mineral LiFePO₄—C LiFePO₄-meltLiFePO₄-triphylite 91.68%  94.01%  Li₃PO₄ 2.05% 0.97% LiFe₅O₈ 1.08%0.00% Li₄P₂O₇ 0.97% 1.67% Fe₃(PO₄)•8H₂O 0.76% 0.00% LiFeP₂O₇ 2.81% 0.00%Li₆P₆O₁₈•H₂O 0.00% 0.70% Li₈P₈O₂₄•6H₂O 0.00% 1.57% Fe₂O₃ 0.65% 0.00%MnO₂-ramsdellite (a) 0.00% 1.08% Total  100%  100% Crystallinity 69.50% 64.90%  (a) MnO₂-ramsdellite phase is a tentative attribution, sincepure Fe samples with no Mn were used for the experiments.

Remarkably also, as shown in Table 1, the LiFePO₄ phase contentincreases from 91.7% to 94% (a 2.54% increase) after the meltingtreatment. It is assumed that this is to be linked to LiFePO₄purification during melting through liquid phase separation andexpulsion of solid impurities like carbon from LiFePO₄—C and otherimpurities or products from secondary reactions resulting for heatingmelting steps. A LECO experiment (C analysis) performed on theLiFePO₄-melt phase confirms the separation of the LiFePO₄ liquid-moltenphase from the carbon coating as LiFePO₄-melt is free of carbon.Concurrently, the XRD analysis of the C crust confirms the presence ofFe₂P associated with some residual LiFePO₄ with a few percent lithiumpyrophosphate and lithiated iron oxides impurities. This first exampleclearly shows the feasibility of preparing LiFePO₄ in the molten statewithout significant decomposition of the material, furthermore, thephase separation observed during the melting process has the beneficialeffect of separating LiFePO₄ liquid phase from residual impurities,carbon if any and decomposition products associated with the highthermal treatment. Another practical benefit of this melting process isto lead to LiFePO₄ in a dense form, crystalline or not depending on thecooling temperature profile. Powdered melted LiFePO₄ has a tap densityof 2.4 as opposed to 1.24 for the original LiFePO₄—C. A high temperatureDSC test was performed on LiFePO₄—C and LiFePO₄-melt, confirming thatLiFePO₄ melts without decomposition, with a broad fusion peak having atop close to 980° C.

Example 2 Electrochemical Characterization of LiFePO₄ Obtained byMelting Process

Electrochemical characterization of the LiFePO₄-melt product of Example1 was made to confirm the performance of the process of the invention. A≈5 g LiFePO₄-melt was thoroughly crushed and grinded in an agate mortar.Subsequently the melted LiFePO₄ powder was C-coated using an organicC-precursor: 1,4,5,8-naphthalenetetracarboxylic dianhydride treatment asdescribed by Marca M. Doeff et al (Electrochemical and Solid-StateLetters, 6(10) A207-209 (2003)). Thus, LiFePO₄-melt (3.19 g) was grindedin a mortar with 1,4,5,8-naphthalenetetracarboxylic dianhydride (0.16 g;product of Aldrich) and 10 ml acetone. After evaporation of acetone, themixed was heated under a CO/CO₂ (50% volume of each gas) flow in arotary chamber placed in an oven. The chamber was first air evacuated byflowing CO/CO₂ during 20 nm at ambient temperature, heated to 650° C.±5°C. in 100 nm and maintained at this temperature for 60 nm and thencooled to ambient temperature. This process gave a carbon coated gradeof LiFePO₄-melt (designated “C—LiFePO₄-melt”) with a 0.33% wt. C-coating(LECO). The C—LiFePO₄-melt has a tap density of 1.9 as opposed to 1.24for the original LiFePO₄—C.

A cathode coating slurry was prepared by thoroughly mixing withacetonitrile, C—LiFePO₄-melt (101.3 mg), polyethylene oxide (product ofAldrich; 82.7 mg), 400,000 molecular weight, and Ketjenblack (product ofAkzo-Nobel; 16.7 mg) carbon powder. This slurry was coated on astainless steel support of 1.539 cm² area whose composition is: 41% wt.polyethylene oxide, 7.46% wt. Ketjenblack and 51.54% wt. C—LiFePO₄-melt.A button type battery has been assembled and sealed in a glove box usinga 1.97 mg active material cathode loading (1.28 mg/cm², 0.78 C/cm²), apolyethylene oxide 5.10⁶ (product of Aldrich) containing 30% wt. LiTFSI(product of 3M) electrolyte and a lithium foil as anode. The battery wasthen tested with a VMP2 multichannel potensiostat (product ofBio-Logic-Science Instruments) at 80° C. with a 20 mV/hr scan speed,between a voltage of 3.0 V and 3.7 V vs Li⁺/Li⁰. Voltametric scans arereported in FIG. 3 while corresponding coulombic data relative totheoretical coulombic value, deduced from weighed active mass, arereported in Table 2. Voltametric scans of C—LiFePO₄-melt (See FIG. 3)are similar to LiFePO₄—C, used in Example 1, in a lithium polymerbattery configuration prepared and tested in the same conditions.

TABLE 2 Coulombic efficiency upon cycling. Cycle Q Charge (Qc) QDischarge (Qd) Qd/Qc Qd/Qd1 #1 96.7% 92.3% 95.4% 100.0% #2 94.7% 91.5%96.5% 99.1% #3 93.0% 89.8% 96.5% 97.3%

This battery test confirms that the electrochemical properties ofC—LiFePO₄-melt are quite equivalent to un-melted LiFePO₄ despite thehigh temperature treatment and the fact that melting leads to more denseand much larger particles than the original un-treated C-coated LiFePO₄.The first discharge coulombic efficiency (92.3%) is closed to the purityof LiFePO₄ phase in LiFePO₄-melt (94.01%). From an active mass (1.97 mg)and first discharge coulombic efficiency (92.3%) a 156.8 mAh/g specificcapacity for LiFePO₄-melt was deduced.

Example 3 Purification of LiFePO₄ by Melting Process

We have obtained from Phostech Lithium Inc a developmental LiFePO₄—Cbatch with very low carbon coating (<0.1% wt.). This LiFePO₄—C was inthe form of brown beads ≈5 mm diameter. After crushing into a powder ina mixer, ≈226 grams of this compound was placed in a 100 oz graphitecrucible and heated in an airtight oven, under a flow of argon gas, fromambient temperatures to 980° C.±5° C. in ≈100 minutes, maintained at980° C.±5° C. during 1 hour and then cooled to ≈50° C. in ≈3 hours.During this step, a ≈225 grams±1 g block of crystalline material with adeep green color and long needle on the surface was obtained. This blockof crystalline material was then crushed in a mortar and then in a ballmill with toluene during 30 minutes. After drying, a pale green powderwas obtained. Then ≈30 grams of this powder, in a 2″ ID graphitecrucible, was again heat treated under the same conditions as for the226 grams batch except that cooling was performed during ≈6 hours. Inthis step, a ≈30 grams±1 g block of crystalline material with a similaraspect as for the 225 grams batch was obtained. XRD spectra of powderhave been performed on LiFePO₄—C, LiFePO₄-melt and LiFePO₄-melt remelteda second time. It appears clearly that as in Example 1, the melt processpreserves the structure of LiFePO₄ and also induced a purification ofthe compound in terms of LiFePO₄ occurrence, from 88.8% for LiFePO₄—C to92.6% for the first melting and 93.7% after two melting processes,corresponding to a 5.5% LiFePO₄ purity increase.

In addition, ICP analysis was performed showing a decrease in sulfurcontent from 1200 ppm for LiFePO₄—C to 300 ppm for the firstLiFePO₄-melt and <100 ppm for the second LiFePO₄-melt.

Example 4 Melting and Purification by Phase Separation of NaturalTriphylite

Even if triphylite ore occurrence is scarce, there was some interest inevaluating the influence of ore melting on its purity. Consequently,some ore was purchased from Excalibur Mineral Corp (Peekskill, N.Y.,USA). The XRD analysis provided in Table 3 indicates that the ore ismainly LiFePO₄ based. A ≈1 cm³ piece of triphylite ore was deposited onan alumina ceramic plate and heated under argon under the sameconditions as those used for the 226 g batch of LiFePO₄—C of Example 3.After this thermal treatment a ≈1″ diameter glossy ore deposit wasobtained in the form of a deep green mound. Interestingly, the mataspect of the top crust seems to indicate a different composition, so itwas decided to determine the distribution of the main elements by X-rayanalysis on a SEM microscope. Thus, the crystalline plate with themelted ore deposit was encapsulated with an epoxy glue and cutperpendicularly to a main diameter with a diamond cutting tool. First,cartographies of top main elements (Fe, O, P, Mn, Mg, Ca, Si, Al) wereestablished and the results are summarized in FIG. 4. This figureclearly indicates that melting of ore induced liquid-liquid phase andliquid-solid phase separation. Well defined crystals of FeO surroundedby a silicium-based melted rich phase and a calcium-based melted richphase can especially be observed. The main phase consists ofLi(Fe,Mn,Mg)PO₄ with relative 25:9:1 atomic ratio of Fe, Mn and Mg, as aconsequence of Mn and Mg miscibility in the LiFePO₄ main liquid. FIG. 5provides mapping of a sample slice for Si, Al and Ca, showing probablymelted or solid phases, dispersed as inclusions in the same mainLi(Fe,Mn,Mg)PO₄ phase or segregated during cooling and solidification.The silicium rich phase is composed of Si, Fe, O, Mn, K, P with arelative atomic ratio between Si, O and P of 68:21:4.5, which probablycontains silicate and phosphate, dispersed in Li(Fe,Mn,Mg)PO₄ with thesame composition as observed at the surface. The calcium rich phase iscomposed of a phosphate containing Ca, Mn, Fe with a relative atomicratio of 25:25:10, possibly as an olivine phase, dispersed inLi(Fe,Mn,Mg)PO₄. The aluminum rich phase is composed of a phosphatecontaining Fe and Al with a relative atomic ratio of 14:7, dispersed inLi(Fe,Mn,Mg)PO₄. This confirms the reorganization of the ore phases uponmelting and the separation of “impure” phases as inclusions. Thoseinclusions can be separated from desired Li(Fe,Mn,Mg)PO₄ main phasedirectly from the melt (phase separation) or after cooling by usualmining processes (crushing, grinding, screening, washing . . . ).

TABLE 3 XRD analysis of Excalibur triphylite ore. Mineral Triphylite OreLiFePO₄-triphylite 63.51% Fe₃(PO₄)₂ 1.92% Fe₃(PO₄)₂-graftonite 4.54%LiAlFPO₄-amblygonite 2.20% KFe₂(OH)(PO₄)₂(H₂O)₂-leucophosphorite 4.19%Li(Mn,Fe)PO₄-sicklerite 4.19% Fe₃(PO₄)₂(OH)₂-lipscombite 14.91%albite-silicate de Na,Ca 2.54% Fe₃O₄-magnetite 1.99% Total 100.00%Crystallinity 60.30%

Example 5 Preparation of LiFePO₄ Directly from FePO₄, Li₂CO₃ andC-Precursor Raw Materials

All previous experiments have clearly established a strong interest forthe fusion process of different forms of synthetic or natural LiFePO₄minerals. In order to extend the scope of this process, we haveinvestigated LiFePO₄ synthesis feasibility directly from raw precursors,FePO₄, Li₂CO₃ and C-precursor, commonly used in LiFePO₄ synthesis inreducing atmosphere as described in WO 02/27823 A1. For this, a premixedprovided by Phostech Lithium Inc of relative molar ratio 2:1FePO₄.2H₂O:Li₂CO₃ with 0.5% wt. C-precursor was used. Two 25 oz graphitecrucibles were filled with a quantity of ≈5 g of this premixed. One ofthe crucibles was filled before with ≈100 mg (≈2% wt.) of pure LiFePO₄powder, obtained in Example 1, to act as a reaction media when in themolten state. Both crucibles were then heated in an airtight oven undera flow of argon from ambient temperatures to 980° C.±5° C. in ≈100minutes, maintained at 980° C.±5° C. during ≈90 nm and then cooled toambient temperature in ≈6 hours. The crystalline material formed wasgray with a metallic aspect and long needles. It was crushed and grindedin a mortar into a grey powder. XRD analysis (See Table 4) indicatesthat both compounds are mainly LiFePO₄, the main difference due topre-synthesized LiFePO₄ addition being a slightly higher yield ofLiFePO₄ and its crystallinity increase from 73.80% to 78.80%.

TABLE 4 XRD analysis of premixed melt under argon at 980° C. with andwithout LiFePO₄ addition. Mineral 0% LiFePO₄ 2% wt. LiFePO₄LiFePO₄-triphylite 91.70% 92.17% FePO₄ 3.22% 2.42% LiFe₅O₈ 1.42% 1.30%Li₄P₂O₇ 0.78% 0.87% LiFe(P₂O₇) 1.61% 1.61% Li₈P₈O₂₄•6H₂O? (a) 0.93%1.30% Fe₃(PO₄)₂(H₂O)₄? (a) 0.34% 0.31% Total 100.00% 100.00%Crystallinity 73.80% 78.80%

Example 6 Preparation of LiFePO₄ Directly from FePO₄ and Li₂CO₃ RawPrecursors

In order to supplement Example 5, LiFePO₄ synthesis feasibility directlyfrom raw precursors, FePO₄ and Li₂CO₃, commonly used in LiFePO₄synthesis in reducing atmosphere as described in WO 02/27823 A1 wasinvestigated. Thus, FePO₄.2H₂O (product of Chemische Fabrik Budenheim KG, Germany; 37.4 g) and battery grade Li₂CO₃ (Limtech Lithium IndustriesInc, Canada; 7.4 g) were thoroughly mixed in a mortar. This mixture wasplaced in a 2″ ID graphite crucible, slightly compressed with a spatula,and then heated in an airtight oven under a flow of argon from ambienttemperatures to 980° C.±5° C. in ≈100 minutes, maintained at 980° C.±5°C. during ≈100 nm and then cooled to ≈50° in ≈3 hours. We have obtaineda pellet of melt mineral of 92.3% LiFePO₄ purity as determined by XRD.This result and Example 5 implied that the melt process is more generalthan just LiFePO₄ purification or the preparation of non C-coatedLiFePO₄ from LiFePO₄—C and allows the preparation from chemicalprecursor of the final compound. This result has clearly confirmed thatthe first surprising LiFePO₄-melt preparation was a major opportunity todesign an improved and simplified alternative industrial process forLiFePO₄ synthesis. Experiment has been repeated under similar conditionswith LiOH, LiCl and LiF as lithium source instead of Li₂CO₃ and in bothcase a LiFePO₄ of >90% purity was obtained.

Example 7 Preparation of LiFePO₄ Directly from Fe₃(PO₄)₂ and Li₃PO₄ RawPrecursors

Fe₃(PO₄)₂.8H₂O (50.16 g) and Li₃PO₄ (product of Aldrich; 11.58 g) werethoroughly mixed in a mortar, poured into an alumina ceramic crucible,and then heated in an airtight oven under a flow of argon from ambienttemperatures to 980° C.±5° C. in ≈100 minutes, maintained at 980° C.±5°C. during ≈60 nm and then cooled to ≈50° C. in ≈3 hours. A battery wasassembled and tested with this material, as described in Example 1, butwithout carbon coating. Electrochemical response was characteristic ofLiFePO₄.

Example 8 Stability of LiFePO₄ to Air Oxidation at 980° C.

Due to surprising results obtained with the melt process, we werecurious to evaluate the stability of pure molten LiFePO₄ to airoxidation at 980° C. So, we placed ≈2 g LiFePO₄, obtained in Example 1,in an alumina ceramic crucible and placed it in an oven heated at 980°C. under air. After 10 nm, the crucible with the molten LiFePO₄ wasquickly soaked in water and the collected mineral was crushed andgrinded in a mortar to obtain a pale green powder. Surprisingly,LiFePO₄, as determined by XRD, is still ≈81% purity (86% of 94% initialpurity). We can conclude from this experiment that it is possible toexpose molten LiFePO₄ during a limited time to air, especially in orderto quench it in a liquid such as water or oil or in a gas by a processsuch as the liquid phase atomization. Another experiment was performedwith exposure time at 980° C. under air of 1 nm instead of 10 nm. Afterquick quenching in water, XRD shows that >95% of the initial LiFePO₄purity was retained. A similar result was obtained by quenching in oilinstead of water.

Example 9 Preparation of LiFePO₄ Directly from Fe₂O₃, (NH₄)₂HPO₄ andLi₂CO₃ Raw Precursors

As the melt process is efficient to produce LiFePO₄ from raw precursor,we have considered the possibility to produce LiFePO₄ from commodityindustrial raw materials in view to reduce materials costs of thesynthesis. Notably, FePO₄ as a chemical specialty represents animportant part of materials cost, we have then decided to rely on aprocess based on Fe₂O₃ as the Fe source. Thus, as first experiment, inan agate mortar, we have thoroughly mixed Fe₂O₃ (product of Aldrich;15.97 g), Li₂CO₃ (product of Limtech; 7.39 g) and (NH₄)₂HPO₄ (product ofAldrich; 26.41 g). This mixture was then placed in a 2″ID graphitecrucible and heated in an airtight oven under a flow of argon fromambient temperature to 980° C.±5° C. in ≈100 minutes, maintained at 980°C.±5° C. during ≈60 nm and then cooled to ≈50° C. in ≈3 hours. XRDanalysis indicates that we have prepared LiFePO₄ with >94% purity. Asecond experiment has been performed with Fe₃O₄ (product of Aldrich;15.43 g) instead Fe₂O₃, with a final >95% LiFePO₄ purity (XRD). A thirdexperiment has been performed with Fe₂O₃ (product of Aldrich; 159.7 g)as Fe sources, Li₂CO₃ (product of Limtech; 73.9 g) and (NH₄)₂HPO₄(product of Aldrich; 264.1 g). Instead of thoroughly mixing thecomponents in a mortar, they were only hand shaken in a 1 liter Nalgenebottle for less than 1 nm. After heat treatment as previously described,LiFePO₄ with >93% purity was obtained. Due to formation of a liquidphase during the synthetic process, intimate mixing of fine particles ofcomponents is not essential to obtain high purity product. A fourthexperiment was performed with same precursors and quantities as in thefirst experiment, but precursors were just weighted directly in a 2″ IDgraphite crucible: Li₂CO₃, Fe₂O₃, and then (NH₄)₂HPO₄ without anymixing. After similar heat treatment as in first experiment, a >90%purity LiFePO₄ was obtained. This experiment has been repeated with(NH₄)H₂PO₄ instead of (NH₄)₂HPO₄ with similar result. Although notoptimized for a short reaction time, this example shows the potentialfor very short reaction time due to efficient mixing and reactionkinetic in the molten state as opposed to presently used synthesisreactions using solids.

Example 10 Preparation of LiFePO₄ Directly from FePO₄ and Li₂CO₃ RawPrecursors

In an agate mortar, we have thoroughly mixed FePO₄.2H₂O (product ofChemische

Fabrik Budenheim K G; 74.8 g) and Li₂CO₃ (product of SQM, Chile; 14.78g). This mixed was then poured into a 100 oz graphite crucible coveredwith another 100 oz graphite crucible and heated in an oven under airfrom ambient temperatures to 980° C.±5° C. in ≈100 minutes, maintainedat 980° C.±5° C. during ≈105 nm and then cooled to ≈100° C. in ≈20 nm.Surprisingly, X-ray diffraction analysis indicates that we have obtainedLiFePO₄ with 89% purity. It is then shown that in the presence of C orin a graphite crucible, even not tightly sealed, it is possible to meltprepare LiFePO₄ under air at 980° C.

Example 11 Preparation of LiMnPO₄ Directly from MnO₂, Li₂CO₃ and(NH₄)₂HPO₄ Raw Precursors

In an agate mortar, we have thoroughly mixed MnO₂ (product of Aldrich;8.69 g), Li₂CO₃ (product of Limtech; 3.69 g) and (NH₄)₂HPO₄ (product ofAldrich; 13.21 g). This mixed was then poured into a 2″ ID graphitecrucible and heated in an airtight oven under a flow of argon fromambient temperatures to 980° C.±5° C. in ≈100 minutes, maintained at980° C.±5° C. during ≈60 nm and then cooled to ≈50° C. in ≈3 hours. XRDanalysis confirms that we have prepared LiMnPO₄ with a >94% purity.

Example 12 Preparation of Li(Fe,Mn)Po₄ Directly from Mno₂, Li₂Co₃ Fe₂O₃and (NH₄)₂HPO₄ Raw Precursors

In an agate mortar, we have thoroughly mixed MnO₂ (product of Aldrich;4.35 g), Fe₂O₃ (product of Aldrich; 3.39 g), Li₂CO₃ (product of Limtech;3.69 g) and (NH₄)₂HPO₄ (product of Aldrich; 13.21 g). This mixed wasthen poured into a 2″ ID graphite crucible and heated in an airtightoven under a flow of argon from ambient temperatures to 980° C.±5° C. in≈100 minutes, maintained at 980° C.±5° C. during ≈60 nm and then cooledto ≈50° C. in ≈3 hours. XRD analysis confirms that we have preparedLi(Mn,Fe)PO₄ with a >90% purity.

Example 13 Preparation of LiFePO₄ Doped by Molybdenum Directly fromFePO₄, Li₂CO₃ and MoO₃ Raw Precursors

In this example we show the possibility of preparing LiFePO₄ doped withMo. In a first experiment (E1), we have thoroughly mixed in an agatemortar FePO₄.2H₂O (product of Chemische Fabrik Budenheim KG; 18.68 g),Li₂CO₃ (product of Limtech; 3.66 g) and MoO₃ (product of Aldrich; 144mg). This mixture was then placed into a 2″ ID graphite crucible andheated in an airtight oven under a flow of argon from ambienttemperatures to 980° C.±5° C. in ≈100 minutes, maintained at 980° C.±5°C. during ≈60 nm and then cooled to ≈50° C. in ≈3 hours. A secondexperiment (E2) has been performed with FePO₄.2H₂O (18.68 g), Li₂CO₃(product of Limtech; 3.58 g) and MoO₃ (432 mg). XRD analyses provided inTable 5 were characteristic of pure LiFePO₄ with respectively 97.8% (E1)and 96.4% (E2) purities. Tentative attributions of Mo phases were alsoprovided.

TABLE 5 XRD analysis for E1 and E2. Mineral E1 E2 LiFePO₄-triphylite97.80% 96.40% Li₃FeMoO₁₂/Li₃Fe(MoO₄)₃ ? 0.95% 0.39% LiMoO₂ ? 0.00% 1.63%LiFe(P₂O₇) 0.83% 1.07% Fe₃(PO₄)₂ ? 0.41% 0.51% Total 100.00% 100.00%Crystallinity 71.90% 69.70%

MEB observation of E2 sample indicates that we have been able to preparea composite material made of LiFePO₄ and a Mo rich phase deposited atgrains boundaries (See FIG. 6). Distribution of E2 main elements,determined by

X-ray analysis in SEM microscope, seems to indicate that Mo interphasewas a Mo rich phosphate phase containing also Fe. We have also observedthat Mo addition reduced size of crystallite. Furthermore, grinding ofE2 sample provides a blue colored powder that might be linked, althoughnot limitatively, to partial dissolution of Mo in LiFePO₄ phase and/orto ionic defects, complexed transition metal ion, or colored centerinduction in the LiFePO₄ crystalline structure.

A battery was assembled and tested with this material, as described inExample 1, but without carbon coating. Electrochemical response wascharacteristic of LiFePO₄ with first charge coulombic efficiency of 76%(129 mAh/g) and first discharge corresponding to 95% of charge capacity(122 mAh/g). However, considering that no C-coating is used, theutilization rate (capacity) is surprisingly high, suggesting a higherelectronic conductivity or Li−ion diffusivity in the Mo-added LiFePO₄phase.

Example 14 Tempering of Mo Doped LiFePO₄

500 mg of the material prepared in Example 13 was sealed under vacuum ina quartz ampula. After heat treatment at 980° C. during 10 nm, theampula was immediately quenched in water. The quenched material wasanalyzed as in Example 13 by microscopy including Mo SEM mapping (SeeFIG. 6). Quenching induces disorder of material and finer distributionbut still keeps a Mo rich phase outside the LiFePO₄ crystal structure.

Example 15 Preparation of LiFePO₄ Doped by Chromium Directly from FePO₄,Li₂CO₃ and Cr₂O₃ Raw Precursors

We intended to explore the possibility of preparing LiFePO₄ doped withCr. In a first experiment (E1), we have thoroughly mixed in an agatemortar FePO₄.2H₂O (18.68 g), Li₂CO₃ (3.58 g) and Cr₂O₃ (product ofAldrich; 76 mg).

This mixed was then poured in a 2″ ID graphite crucible and heated in anairtight oven under a flow of argon from ambient temperatures to 980°C.±5° C. in ≈100 minutes, maintained at 980° C.±5° C. during ≈80 nm andthen cooled to ≈50° C. in ≈3 hours. A second experiment (E2) wasperformed with FePO₄.2H₂O (18.68 g), Li₂CO₃ (3.36 g) and Cr₂O₃ (228 mg).XRD analyses (See Table 6) were characteristic of LiFePO₄ withrespectively 91.5% (E1) and 89.2% (E2) purities but show the presence ofelectronically conductive metallic Cr.

TABLE 6 XRD analysis for E1 and E2. Mineral E1 E2 LiFePO₄-triphylite91.53% 89.17% Fe₃O₄ 0.32% 0.83% LiFe(P₂O₇) 2.89% 4.36% Li₈P₈O₂₄•6H₂O2.00% 2.25% Cr 2.00% 2.50% FeO 0.37% 0.29% Carbon 0.89% 0.59% Total100.00% 100.00% Crystallinity 70.60% 69.80%

Example 16 Preparation of LiFePO₄ Directly from FePO₄ and Li₂CO₃ RawPrecursors Under CO/CO₂ Atmosphere in the Absence of C Additive orGraphite Crucible

We have thoroughly mixed in an agate mortar FePO₄.2H₂O (37.37 g) andLi₂CO₃ (7.39 gr). This mixed was then placed in an alumina ceramiccrucible and heated in an airtight oven under a flow of CO/CO₂ (3:1)from ambient temperatures to 980° C.±5° C. in ≈100 minutes, maintainedat 980° C.±5° C. during ≈60 nm and then cooled to ≈50° C. in ≈3 hours. Abattery was assembled and tested with this material, as described inExample 1, but without carbon coating. Electrochemical response wascharacteristic of LiFePO₄.

Example 17 Preparation of LiFePO₄ Directly from Fe₂O₃, (NH₄)₂HPO₄ andLi₂CO₃ Raw Precursors Under Inert Atmosphere and in the Absence of CAdditive or Graphite Crucible

We have thoroughly mixed in an agate mortar Fe₂O₃ (15.98 g), Li₂CO₃(7.39 g) and (NH₄)₂HPO₄ (26.4 g). This mix was then poured in an aluminaceramic crucible and heated in an airtight oven under a flow of argonfrom ambient temperatures to 980° C.±5° C. in ≈100 minutes, maintainedat 980° C.±5° C. during ≈60 nm and then cooled to ≈50° C. in ≈3 hours. Abattery was assembled and tested with this material, as described inExample 1, but without carbon coating. Electrochemical response wascharacteristic of LiFePO₄.

Example 18 Preparation of LiFePO₄ Directly from Fe₂O₃ and LiH₂PO₄ RawPrecursors Under Inert Atmosphere Starting from a Fe+3 Reactant WithoutC Additive or Graphite Crucible:

We have thoroughly mixed in an agate mortar Fe₂O₃ (15.98 g) and LiH₂PO₄(product of Aldrich; 20.8 g). This mix was then poured in an aluminaceramic crucible and heated in an airtight oven under a flow of argonfrom ambient temperatures to 980° C.±5° C. in ≈100 minutes, maintainedat 980° C.±5° C. during ≈60 nm and then cooled to ≈50° C. in ≈3 hours. Abattery was assembled and tested with this material, as described inExample 1, but without carbon coating. Electrochemical response wascharacteristic of LiFePO₄ showing that thermal reduction of Fe+3 into alithiated iron+2 phosphate is possible.

Example 19 Preparation of LiFePO₄ Directly from Fe, Fe₂O₃ and LiH₂PO₄Raw Precursors Under an Inert Atmosphere in the Absence of C Additive orGraphite Crucible but in the Presence of Fe° as a Reducing Agent

We have thoroughly mixed in an agate mortar Fe (product of Aldrich; 5.58gr), Fe₂O₃ (15.97 g) and LiH₂PO₄ (31.18 g). This mix was then poured inan alumina ceramic crucible and heated in an airtight oven under a flowof argon from ambient temperatures to 1000° C.±5° C. in ≈100 minutes,maintained at 1000° C.±5° C. during ≈60 nm and then cooled to ≈50° C. in≈3 hours. A battery was assembled and tested with this material, asdescribed in Example 1, but without carbon coating. Electrochemicalresponse was characteristic of LiFePO₄.

Example 20 Preparation of LiFePO₄ Directly from Fe and LiH₂PO₄ RawPrecursors Under a CO/CO₂ Atmosphere

We have thoroughly mixed in an agate mortar Fe powder (11.17 g) andLiH₂PO₄ (20.79 g). This mix was then poured in an alumina ceramiccrucible and heated in an airtight oven under a flow of CO/CO₂ fromambient temperatures to 980° C.±5° C. in ≈100 minutes, maintained at980° C.±5° C. during ≈60 nm and then cooled to ≈50° C. in ≈3 hours. Abattery was assembled and tested with this material, as described inExample 1, but without carbon coating. Electrochemical response wascharacteristic of LiFePO₄. This example shows that a buffered gasmixture such as CO/CO2 can oxidize Fe° to Fe+2 in the conditions of theprocess of the invention.

Example 21 Preparation of Magnesium Doped LiFePO₄ Directly from Fe₂O₃,Li₂CO₃, (NH₄)₂HPO₄ and MgHPO₄ Raw Precursors

We have thoroughly mixed in an agate mortar Fe₂O₃ (15.17 g), Li₂CO₃(7.39 g), (NH₄)₂HPO₄ (25.09 g) and MgHPO₄ (product of Aldrich. 1.2 g).This mix was then poured in a 2″ ID graphite crucible and heated in anairtight oven under a flow of argon from ambient temperatures to 980°C.±5° C. in 100 minutes, maintained at 980° C.±5° C. during 60 nm andthen cooled to 50° C. in ≈3 hours. XRD and ICP analysis indicates thatwe have obtained LiFe_(0.95)Mg_(0.05)PO₄ olivine solid solutionwith >90% purity.

Example 22 Preparation of LiFePO₄ Directly from Fe₂O₃ and LiH₂PO₄ RawPrecursors

We have thoroughly mixed in an agate mortar Fe₂O₃ (15.98 g), LiH₂PO₄(20.8 g) and EBN1010 graphite powder (product of Superior Graphite; 1.2g). This mix was then placed in an alumina ceramic crucible and heatedin an airtight oven under a flow of argon from ambient temperatures to980° C.±5° C. in ≈100 minutes, maintained at 980° C.±5° C. during 60 nmand then cooled to ≈50° C. in 3 hours. We have obtained a crystallinematerial with a small crust mainly composed of carbon at its surface.Ceramic has been identified by XRD as LiFePO₄ of >90% purity. A secondsimilar experiment has been performed with same quantities of Fe₂O₃ andLiH₂PO₄ but with 600 mg of graphite instead of 1.2 g. Thus, we haveobtained a >90% purity LiFePO₄.

Example 23

Electrochemical characterization of LiFePO₄:A 2 kg quantity of LiFePO₄(94% purity by XRD) was prepared, in several batches, as disclosed inthe first experiment of Example 9 from Fe₂O₃, (NH₄)₂HPO₄ and Li₂CO₃.Those 2 kg were summarily crushed in an alumina mortar in the form of ≈1mm chunk. A batch of LiFePO₄ was further ground with a planetary mill PM100 (Product of Retsch GmbH & Co. KG, Germany). Thus, 200 g of LiFePO₄were wet milled during 10 nm with 12 g of 20 mm zirconia balls in azirconia jar and further during 90 nm with 440 g of 3 mm zirconia balls,in both case with 90 cc iso-propanol. Particle size and distribution isprovided in Table 7, mean size was 1.44 μm.

TABLE 7 Size distribution after planetary mill milling Diameter on %Size (μm) Size (μm) % on Diameter 5% 0.38 100  100% 10% 0.43 50  100%20% 0.54 5 99.4% 30% 0.72 1 40.8% 40% 0.98 0.5 16.6% 60% 1.46 0.1   0%70% 1.75 80% 2.15 90% 2.83 95% 3.44

20 gr of planetary mill ground LiFePO₄ were mixed with 6% wt. celluloseacetate (product of Aldrich) dissolved in acetone. This mixture was thendried and treated at 700° C. for 1 hour under an argon atmosphere,quantity of carbon remaining in the material was 1.23% wt. as determinedby elementary analysis. Composite cathodes electrodes were prepared withthe carbon-coated material, EBN1010 (product of Superior Graphite) asconductive agent and PVdF as binder in 80/10/10 wt. proportions. Densityof these coatings was 1.7, instead of 1.2 with similar coating usingLiFePO₄—C disclosed in Example 1, corresponding to a 40% increase of thecoating density. Electrochemical performances of cathode coating wereinvestigated at room temperature in coin cell battery using metalliclithium as anode and 1M LiClO₄ in EC:DMC (1:1) impregnated in 25 μmpolypropylene Celgard® as electrolyte. Cathode surface was 1.5 cm² with4.4 mg/cm² LiFePO₄ loading. A first slow scan voltametry (20 mV/h),between a voltage of 3.0 V and 3.7 V vs Li⁺/Li⁰ was performed at ambienttemperature with a VMP2 multichannel potensiostat (product ofBio-Logic-Science Instruments). Power tests were further performed byintentiostatic experiment (See FIG. 7), rates were calculated from thespecific capacity value obtained from first slow scan voltametry (159.9mAh/g). LiFePO₄ prepared from low cost precursors by melt process andgrinded by currently available milling machinery can sustain high rates.

Alternative grinding was also performed with a laboratory Jet-Mill,adjusting conditions (time, air flow, . . . ), to obtain a LiFePO₄powder with 1 to 5 μm mean size.

Of course, the above description of the embodiments of the invention isnot limitative and also comprises all possible variations andembodiments that may seem obvious to a man skilled in the art.

1. Process for preparing an at least partially lithiated transitionmetal oxyanion-based lithium-ion reversible electrode material, whichcomprises providing a precursor of said lithium-ion reversible electrodematerial, heating said precursor, melting same at a temperaturesufficient to produce a liquid phase comprising an at least partiallylithiated transition metal oxyanion, and cooling said liquid phase underconditions to induce solidification of an at least partially lithiatedtransition metal oxyanion electrode material in a pure, partiallysubstituted or doped form, wherein said solid electrode material isreduced to powder form or agglomerate of particles by high-energy wetball milling.
 2. A process according to claim 1, wherein prior to saidhigh-energy milling, said process comprises pre-milling said solidelectrode material to produce about millimeter size powder.
 3. A processaccording to claim 1, wherein said high-energy wet ball milling isperformed with milling balls having a size of about 3 to about 20 mm. 4.A process according to claim 1, wherein said high-energy wet ballmilling is performed with zirconia milling balls.
 5. A process accordingto claim 1, wherein said high-energy wet ball milling is performed withmilling balls, using a solid electrode material:balls ratio (wt./wt.) ofabout 0.4:1 to about 17:1.
 6. A process according to claim 1, whereinsaid high-energy wet ball milling is performed for a time duration ofabout 10 minutes to about 90 minutes.
 7. A process according to claim 1,wherein said solid electrode material is reduced to a powder having anindividual mean particle size between 20 nanometers and 5 microns andagglomerate mean particle size between 100 nanometers and 15 microns. 8.A process according to claim 7, which comprises externally treating theindividual particles or agglomerates by chemically or mechanicallyapplying carbon (C) or other chemical additive used in a battery.
 9. Aprocess according to claim 1, wherein said lithium-ion reversibleelectrode material has the nominal formula AB(XO₄)H, wherein A islithium, which may be partially substituted with another alkali metalrepresenting less than 20% at. of said A; B is a main redox metal atoxidation level of +2 selected from the group consisting of Fe, Mn, Ni,and any mixtures thereof, which may be partially substituted by one ormore additional metal at oxidation level between +1 and +5 andrepresenting less than 35% at. of said main +2 redox metal, including 0;XO₄ is any oxyanion wherein X is selected from the group consisting ofP, S, V, Si, Nb, Mo, and any combinations thereof; and H is a fluoride,hydroxide or chloride anion representing less that 35% at. of the XO₄oxyanion, including
 0. 10. A process according to claim 9, wherein A islithium, partially substituted with another alkali metal representingless than 20% at. of said A.
 11. A process according to claim 9, whereinA is lithium.
 12. A process according to claim 9, wherein B is a mainredox metal at oxidation level of +2 selected from the group consistingof Fe, Mn, Ni, and any mixtures thereof, partially substituted by one ormore additional metal at oxidation level between +1 and +5 andrepresenting less than 35% at. of said main +2 redox metal, including 0.13. A process according to claim 9, wherein B is a main redox metal atoxidation level of +2 selected from the group consisting of Fe, Mn, Ni,and any mixtures thereof.
 14. A process according to claim 9, whereinXO₄ is PO₄.
 15. A process according to claim 9, wherein said lithium-ionreversible electrode material has the nominal formula AB(XO₄).
 16. Aprocess according to claim 9, wherein said lithium-ion reversibleelectrode material has the nominal formula AB(PO₄).
 17. A processaccording to claim 9, wherein said lithium-ion reversible electrodematerial has the nominal formula LiB(PO₄).
 18. A pure, partiallysubstituted or doped lithium-ion reversible electrode material havingthe nominal formula AB(XO₄)H in which: A is lithium, which may bepartially substituted with another alkali metal representing less than20% at. of said A; B is a mixture of redox metals at oxidation level of+2 comprising Fe, Mn, and another metal at oxidation level +2; XO₄ isany oxyanion wherein X is selected from the group consisting of P, S, V,Si, Nb, Mo, and any combinations thereof; and H is a fluoride, hydroxideor chloride anion representing less that 35% at. of XO₄, including 0.19. The electrode material according to claim 18, wherein the othermetal at oxidation level +2 is Mg.
 20. The electrode material accordingto claim 19, comprising about 2% of Mg (wt./total wt. of B).
 21. Theelectrode material according to claim 18, comprising at least about 70%of Fe (wt./total wt. of B).
 22. The electrode material according toclaim 18, comprising at least about 20% of Mn (wt./total wt. of B). 23.The electrode material according to claim 18, wherein A is lithium,partially substituted with another alkali metal representing less than20% at. of said A.
 24. The electrode material according to claim 18,wherein A is lithium.
 25. The electrode material according to claim 18,wherein XO₄ is PO₄.
 26. The electrode material according to claim 18,having the nominal formula Li(Fe,Mn,Mg)PO₄.
 27. A pure, partiallysubstituted or doped lithium-ion reversible electrode material havingthe nominal formula LiB(PO₄) in which B is a mixture of redox metals atoxidation level of +2 comprising Fe, Mn and Mg.
 28. The electrodematerial according to claim 18, having a pyrolytic carbon deposit. 29.The electrode material according to claim 26, having a pyrolytic carbondeposit.
 30. The electrode material according to claim 27, having apyrolytic carbon deposit.
 31. A cathode electrode comprising theelectrode material according to claim
 28. 32. A cathode electrodecomprising the electrode material according to claim
 29. 33. A cathodeelectrode comprising the electrode material according to claim 30.